Browsing by Author "Henen, Brian T."

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    Body of evidence: forensic use of baseline health assessments to convict wildlife poachers
    (CSIRO Publishing, 2013) Henen, Brian T.; Hofmeyr, Margaretha D.; Baard, Ernst H. W.
    CONTEXT. Given the immense impact of wildlife trade, disease and repatriations on populations, health assessments can" "provide powerful forensic material to help convict wildlife poachers and minimise risks of releasing unhealthy wildlife." AIMS. We aimed to use reference ranges to assess the health of confiscated tortoises, to illustrate forensic application of these ranges, and to advance analyses for future applications." METHODS. We used analyses of variance (ANOVA) and covariance (ANCOVA), and composite indices, to compare wild and confiscate tortoise body condition, haematocrit and haemoglobin concentration of males and females of three tortoise species. Subsequently, we used multivariate statistics (e.g. discriminant analyses) to evaluate the relative importance of species, sex and group (wild or confiscate) on tortoise condition and haematology." KEY RESULTS. Our initial statistical tests demonstrated, at P < 0.05 to P < 0.0005, that confiscate body condition and haematology were compromised compared with that of wild tortoises. Subsequently, discriminant analyses strongly discriminated between most wild and confiscate groups (P < 0.0001), correctly classified individual health as wild or confiscate 80–90% of the time, indicated that species and sex effects were stronger than was the wild-confiscate category, and provided discriminant functions for use on other taxa and studies." CONCLUSIONS. The health assessments discriminated well between wild and confiscate tortoises. The results had considerable forensic value, being relevant, quickly generated using portable field equipment, reliable, accurate, easy to explain and convey in terms of likelihood in a court of law, synergistically consistent among variables and groups, a strong rebuttal to the poachers’ specific statements, and consistent with other types of evidence. Multivariate analyses were consistent with, and more prudent and powerful than, the original statistical analyses. Discriminant functions can be applied in future studies and on other chelonian species, and should be developed for other wildlife species." IMPLICATIONS. Reference ranges provide considerable value for forensics, diagnostics and treatment. Given the disease risks resulting from the massive scale of wildlife trade and release, reference ranges should be developed for more species."
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    Seasonal effects on the feeding ecology and habitat of Chersina Angulata in the South Western Cape
    (University of the Western Cape, 2008) Joshua, Quinton Ignatius; Hofmeyr, Margaretha D.; Henen, Brian T.
    Nearly one-third of the world’s tortoises live in South Africa, but little is known about their habitat requirements and feeding ecology. Chersina angulata, the angulate tortoise, is endemic to southern Africa, with a wide distribution along the western and southern coasts. Because this tortoise occupies a number of different habitat types, it has always been considered a generalist herbivore, although little is known about its diet and other needs. This study evaluates the habitat characteristics and feeding ecology of C. angulata at two study sites in the southwestern Cape, the West Coast National Park (WCNP) and Dassen Island (DI). The WCNP is a large conserved area in the Fynbos biome, along the southwestern coast of South Africa, whereas DI is a small offshore island with low floral and faunal diversity, just south of the WCNP. The efficacy of three methods used to study the feeding ecology of herbivores, focal observations, macroscopic faecal analysis and histological analysis of scats, was evaluated. Plant cover, species diversity, and the variety of growth forms were substantially larger at the WCNP than on DI. In the WCNP, shrubs and grasses were the dominant growth forms but the vegetation also included herbs, succulents, restios, sedges and parasitic plants. A few perennial species such as the grass Ehrharta villosa, shrubs such as Helichrysum niveum, Nylandtia spinosa and Rhus spp., and succulents such as Carpobrotus edulis and Ruschia spp., provided most of the plant cover. DI had a depauperate flora, consisting of succulents and herbs, and ephemeral plants contributed more than perennials did to plant cover throughout the year. The succulents Mesembryanthemum crystallinum and Tetragonia fruticosa provided most of the cover on DI. Angulate tortoises are herbivores and 72 diet plants in 32 plant families were identified to the species or genus level. Several diet species, however, could not be identified. In addition to angiosperms, the tortoises’ diet included mosses, mushrooms, insects,snails and animal faeces. The most important growth forms in the diet were herbs and grasses. The diet of the WCNP tortoises was more diverse than the diet of DI tortoises, but the number of principal food items in the diet did not differ between the two sites. Over an annual cycle, WCNP tortoises had four principal food plants while DI tortoises had five principal food plants. At both sites, principal food plants changed with the season and few plants remained principal food items in more than one season. Cynodon dactylon was a principal food item in three of the four seasons in the WCNP, whereas Trachyandra divaricata was a principal food plant each season on DI. Most principal food plants were grass or herb species but the sedge Ficinia nigrescens, and a succulent that could be identified only to the family level (Aizoaceae), featured strongly in the spring diets of DI and WCNP tortoises, respectively. The three study methods did not provide the same type or quality of information about the feeding ecology of angulate tortoises. The small size and wary nature of angulate tortoises compromised focal studies because it was often not possible to see what the tortoises ate. This method, however, provided the interesting observation that rabbit faecal pellets contributed nearly 30% to summer and autumn diets on DI when food was scarce. Rabbit faeces may not only provide a source of nutrients but may also supplement the microflora, required to digest cellulose, in the tortoises’ guts. Macroscopic evaluation of the tortoises’ scats appeared to be an ineffective method to identify diet plants, and the bulk of the scat mass could not be identified. This indicates that angulate tortoises either selected food low in fibrous content or that the digestive system of the tortoises dealt efficiently with tough plant material. The macroscopic method was the only method that highlighted the large contribution of fruits / seeds to the diet of angulate tortoises. Since the tortoises digested many seeds only partially, or not at all, C. angulata is potentially an important agent of seed dispersal in the southwestern Cape. The macroscopic study showed that on DI, sand made up 28% of the scat mass in spring, whereas sand never made a substantial contribution to the scat composition of WCNP tortoises. Lithophagy may be an important strategy in a depauperate habitat, such as DI, because the abrasive action of sand may help with the digestion of tough plants, or the sand may provide the tortoises with important minerals that are deficient in their food plants.The histological analysis of scats provided the most comprehensive diet list for C. angulata. Selection indices based on data from the histological analysis indicated that angulate tortoises were highly selective in their food choice. Most of the principal food items were selected out of proportion to their availability and the tortoises avoided the most abundant plants in their habitats. Several factors, such as palatability, accessibility and profitability, may have influenced their food choice. The proportional similarity indices for WCNP and DI tortoises, respectively, were 0.31 and 0.16, confirming that C. angulata is a food specialist and not a food generalist as was previously thought. This factor should be considered in the management of this species and in future conservation planning of its habitat.
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    Seasonal movement and activity patterns of the endangered geometric tortoise, psammobates geometricus
    (University of the Western Cape, 2005) Van Bloemestein, Ulric Patrick; Hofmeyr, Margaretha D.; Henen, Brian T.; Dept. of Biodiversity and Conservation Biology; Faculty of Science
    Due to the critical status of Psammobates geometricus and the vulnerability of their habitat, there is a need to allocate areas for their protection. The aim of this study was to provide information on the space requirements and activity level of geometric tortoises to facilitate future conservation efforts. The thread-and-spool method was used to compare short-term movements, habitat utilisation, and activity patterns of male and female tortoises over 15 and 20 days respectively, in autumn and spring. Through radiotelemetry, the long-term movements of 10 male and 11 female tortoises were evaluated from April 2002 to April 2003. Locality data for the short-term and long-term studies were used to calculate the size of activity areas and home ranges as minimum convex polygons and fixed kernel estimates. Male and female geometric tortoises were active throughout the year, and maintained a high level of activity in autumn and in spring. However, females were more active than males were in spring. Females may require more resources, particularly food, in spring when they produce eggs. Although males and females travelled similar distances in autumn and in spring, males displaced further than females displaced in both seasons. The movement path for males was often linear, perhaps because this path may enhance their opportunities to encounter females. Geometric tortoise males were substantially smaller than females, which may explain why the distances that males moved and displaced in spring were negatively correlated to environmental temperature. In autumn, when temperatures were lower than in spring, the distance travelled by males was not correlated to temperature. However, in autumn female displacement showed a positive correlation with environmental temperature. Geometric tortoises showed large inter-individual variation in home range size, which may contribute to the fact that home range size did not differ among the three different habitat types: mature renosterveld, burned renosterveld and the old agricultural fields. Average home range size was 11.5 ha for 95% fixed kernel estimates, and 7.0 ha for minimum convex polygon estimates. Body size influenced the home range size of female geometric tortoises, but had no effect on the home range size of male tortoises. Females had larger home ranges than male tortoises had, possibly because females were larger, but reproductive requirements of females may have played a role. During the dry season, home range size increased when compared to the wet season. The larger home range during the dry season, which is associated with high temperatures, may be related to a reduction in resource availability. The fewer resources available, the greater the distance the tortoises would need to travel in order to acquire the necessary resources. The small home range in the wet season may indicate an abundance of resources, but it may also be that large pools of standing water restrict the movements of tortoises. Understanding the spatial and habitat requirements of P. geometricus will help to assess the viability of populations in disturbed and highly fragmented areas, and contribute to the conservation efforts for this endangered species.
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    Variation in the daily activity, movement and refugia of Critically Endangered geometric tortoises, Psammobates geometricus, in autumn and spring
    (Taylor & Francis, 2017) Henen, Brian T.; van Bloemestein, Ulric P.; Hofmeyr, Margaretha D.; Weatherby, Craig A.
    To help assess habitat requirements of Critically Endangered geometric tortoises, we used thread-trailing to measure daily activity, movements and refugia of adult Psammobates geometricus in autumn and spring 2002. We found strong differences between seasons, and effects of weather, individuals and sex. The high activity was consistent with mild weather during autumn and spring. However, daily temperatures limited female movements on cool autumn days and male movements on warm spring days, a pattern consistent with sexual size dimorphism (large females and small males). The long movements in autumn probably helped tortoises find food plants that grow quickly after autumn rains; both sexes recover body condition from autumn lows, and females begin egg production in late-autumn and winter. These movements may also help males mate with females before they ovulate. The high activity of females in spring should help them forage and sustain their vitellogenesis, egg production and nesting in spring. Male paths tended to be more linear than female paths in both seasons, so this sexual difference is likely not linked to food consumption. Males may move long, linear paths to engage females and avoid other males. Males may have been thermally-challenged in spring. Their movements decreased with increased ground temperatures (in the sun), they used denser refugia in spring than in autumn, and in spring used denser refugia than females used. Geometric tortoises typically used different refugia on consecutive nights, a type of predator avoidance mechanism.